The Queensland fruit fly (Bactrocera tryoni), also known as Q-fly and QFF, is common in towns and horticultural areas throughout eastern Australia. It was introduced into New Caledonia around 1969 and French Polynesia around 1970. It is now widespread in New Caledonia, French Polynesia and Pitcairn Islands. It was introduced but eradicated from Perth (Western Australia) and Easter Island in the mid-Pacific. More recently, it was detected in Rarotonga, Cook Islands, on the 21st November 2001. Its detection prompted a quick emergency response. The Q-fly is very destructive to a large range of fruit hosts, and has significant economic impacts on the areas in which it lives.

DescriptionThe adult Queensland fruit fly (Q-fly) is about 7 mm long. It has a wing span of 10 – 12 mm. They are a reddish brown colour, with yellow markings. Its “abdomen is constricted at the base, flared in the middle, and broadly rounded at the tip” (Weems & Fasulo, 2007). The female has a retractable ovipositor at the tip of her abdomen, with which she can lay several hundred eggs during her lifetime inside maturing and ripe fruit. Q-flies can move quickly if disturbed. They are usually found either on maturing fruit, or on the underside of leaves (Dominiak, 2007a). Larvae, which can be up to 10mm long, emerge from the eggs relatively quickly, and cause damage inside the fruit by feeding inside it for a number of days. The infested fruit can appear to be undamaged.

General impactsThe Queensland fruit fly is the most costly and serious insect pest effecting agriculture in Australia. It infests all commercial fruit crops in Australia, other than pineapple and strawberry. The majority of an estimated A$100 million a year potential losses if fruit flies were not controlled in Australia would be caused by Queensland fruit fly (Botha et al. 2000).

The Queensland fruit fly (Q-fly) lays its eggs in a wide range of maturing or ripe fruit. The maggots, which hatch from the eggs inside the fruit, tend to destroy the fruit, either due to their feeding, or decaying. The Q-fly is such a problem as it has a large number of host fruits world-wide, and has a fairly wide climatic tolerance.

Research has found that the Q-fly can displace other Bactrocera fruit flies (Bactrocera tryoni and Bactrocera kirki) in coastal areas (Vargas et al. 2007).

Geographical rangeThe Queensland fruit fly (Q-fly) “permanently inhabits parts of the Northern Territory, Queensland, New South Wales and the eastern corner of Victoria” in Australia (DPI, 2008). The Q-fly is common in towns and horticultural areas throughout eastern Australia (Gilchrist, pers. Comm.. 2008). It was introduced into New Caledonia around 1969 and French Polynesia around 1970. It is now widespread in New Caledonia, French Polynesia and Pitcairn Islands. Studies have found that very few Q-flies survive the winter at high altitude, and so there is “an annual colonisation of the higher altitudes by flies from the lower altitudes” (Drew & Hooper, 1983).

While most tropical fruit fly species in Australia are negatively impacted by the conversion of indigenous rainforest (which they are native to) into agricultural and suburban areas, studies have shown that the Queensland fruit fly was “positively affected by transformation of natural habitat into suburbia,” due its abilities to use widely available novel habitats (Raghu et al. 2000). According to Dominiak et al. (2006): “for the Queensland fruit fly, towns appear to be oases compared with the surrounding rural desert.” This study goes on to conclude that while low temperatures limit Q-fly populations over winter, moisture levels over Summer in a specific area determine how well Q-fly will thrive there. Even a small amount of irrigation over the summer months, common in urban areas, contributed to counteracting the negative effects of low moisture found during the height of summer, increasing the survivability of Q-fly over the summer period.

The Q-fly is able to overwinter due to its ability to reacclimatise to a gradually cooling temperature. Studies have shown (Meats, 1973) that Q-flies can reacclimatise continuously to a falling temperature, as long as the drop is not faster than 1°C per minute. The temperature range which the Q-fly can survive is atleast -2°C to 25°C, and may even be larger than this. However, acclimatisation to low temperatures cannot prevent frost-induced extinctions when the minimum temperatures in a location fall below -4.5°C (Meats, 1976).

Introduction pathways to new locationsAgriculture:Ignorant possession:Natural dispersal: Studies on the dispersal range of laboratory-reared irradiated adult Queensland fruit flies have proven that Q-flies are able to disperse up to 94 km. A number of the most distant traps used in this study “caught more than one fly, indicating that the flies moved together over long distances. This suggests that mating could occur and that new infestations could result from the long-distance migration of adults” (MacFarlane, 1987). On average, however, the majority of studies show that Q-flies rarely disperse over 1km (Dominiak et al. 2003b). The “short-range dispersal patterns” of adult male and female Q-flies are the same (Weldon & Meats, 2007). A large amount research on the dispersal patterns of Q-fly has been undertaken. Meats & Edgerton (2008) have recently found that the size of an infestation is a key factor in determining the longevity of an infestation, and its potential to spread successfully.

Local dispersal methodsAgriculture (local):Natural dispersal (local):

Management informationPreventative measures: Early detection of an outbreak of any invasive species is very important, as it increases the odds of a successful eradication, before the pest becomes established. In South Australia there is an ‘early warning system’ of traps to detect outbreaks of adult Q-flies. “A grid of more than 3800 fruit fly trapping sites in metropolitan Adelaide, Northern Adelaide Plains, Adelaide Hills, Riverland and a number of country towns are checked regularly by PIRSA officers” (Heaven, 2007). There is also a ‘Fruit Fly Hotline’ for the public to report possible discoveries of Q-fly.

In New Zealand, an annual fruit fly surveillance trapping program is undertaken by MAF Biosecurity New Zealand (MAFBNZ) to detect any incursions of fruit flies, including the Q-(MAFBNZ, 2008b).There are over 7500 traps used nationwide in this surveillance, and they are “concentrated in populated areas serving as centers for tourism and/or trade, areas of significant horticultural activity and areas specified as being climatically conducive to the establishment of fruit fly” http://www.biosecurity.govt.nz/pests/queensland-fruit-fly (MAFBNZ, 2008a).

Integrated management: As with the control of many pest species, a single control method by itself is often not sufficient to eradicate (or even effectively control) the Queensland fruit fly (Q-fly) from an area. The best results are gained from a combination of the methods found in the section below. For example, bait spraying, male annihilation and good hygiene have been used in combination in attempts to eradicate Q-fly in New South Wales, Australia (Gilchrist, pers. Comm. 2008).

NutritionOver 100 species of fruits and vegetables can act as hosts of the Queensland fruit fly. “Adults feed primarily upon juices of host plants, nectar, and honeydew secreted by various kinds of insects” (Weems & Fasulo, 2007).

ReproductionThe Queensland fruit fly mates at dusk (Raphael et al. 2004). Female Q-flies have been found to be poor at detecting a difference between the numbers of calling males, in groups of different sizes (Weldon, 2006). The Q-fly does not mate continuously throughout the year, but it passes the winter in the adult stage. The total life cycle of the Q-fly requires 2 weeks in summer but up to 2 months in autumn. Adult females usually live for a number of months (Weems & Fasulo, 2007).

Lifecycle stagesEgg: Normally about six white, banana-shaped eggs are laid in a flask-shaped chamber, which is dug out about 3mm deep in the outer layer of host fruit (Dominiak, 2007a).Larva (maggot): The eggs normally hatch after 2 or 3 days (MAFBNZ, 2008a), and a small maggot emerges from each egg. These maggots use eat towards the centre of the fruit, utilising their sharp cutting jaws. The fruit can continue to look perfect from the outside while this is happening on the inside. Maggots have cutting jaws which help to tear the fruit into pieces small enough to swallow. Maggots tend to eat towards the centre of the fruit. This also promotes rotting of the fruit, although it may look perfect from the outside (DPI, 2008). The larvae are usually feeding inside the fruit for 10 to 31 days after hatching (MAFBNZ, 2008a). After its growth is completed, the maggot eats its way out of the fruit, which has by now usually fallen onto the ground, and burrows into the soil (DPI, 2008). Up to 70 individuals can develop from a single fruit (MAFBNZ, 2008a).Pupa: After the larvae enter the soil, they become inactive and change into brown, hard, oval-shaped pupae, in which the adult fly develops (DPI, 2008). Pupal development time varies from a week in Summer to over a month in Winter (Weems & Fasulo, 2007). High levels of pupal mortality occur at high and low extremes of soil moisture (Hulthen & Clarke, 2006).Adult (fly): After emerging from the pupae, adult flies first find a food source. After feeding, flies search for a mate, and mating occurs. After “passing through a two-week pre-oviposition stage following emergence from the pupae” (Weems & Fasulo, 2007), females then look for ripening fruit. She then either punches a hole into the fruit, in which she lays groups of up to 7 eggs. Q-fly females often use existing punctures within fruit (DPI, 2008). Studies have shown that Q-flies “prefer to oviposit in existing punctures rather than drill a fresh puncture” (Prokopy et al. 1991). Female fruit flies can lay between 500 and 800 eggs in the duration of their life, which can last anywhere from 6 months to a year (Heaven, 2007).

Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG) with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment

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